1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays, gamma-rays, and the like).
2. Description of the Prior Art
Photoconductive materials which constitute photoconductive layers for solid state image pick-up devices, electrophotographic image-forming member in the field of image formation, or manuscript reading devices, are required to have a high sensitivity, a high SN ratio (Photocurrent (I.sub.p)/Dark current (I.sub.d)), spectral characteristics matching those of the electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon (hereinafter referred to as a-Si) has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German Laid-Open Patent publication No. 2933411 an application of a-Si for use in a photoelectric converting reading device.
However, under the present situation, while the photoconductive members having photoconductive layers constituted of a-Si have been attempted to be improved in various aspects individually including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and environmental characteristics, and further stability with lapse to time and durability, there remains room for further improvement of overall characteristics.
For instance, when applied in an image forming member for electrophotography, residual potential is frequently observed to remain during use thereof if improvements to higher photosensitivity and higher dark resistance are scheduled to be effected at the same time. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigues by repeated uses or a so-called ghost phenomenon wherein residual images are formed.
Further, a-Si materials may contain as constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics, boron atoms, phosphorus atoms, etc. for controlling the electroconduction type as well as other atoms for improving other characteristics. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused problems with respect to electrical, photoconductive characteristics or dielectrical strength of the layer formed.
That is, for example, when used as an image forming member for electrophotography, the life of the photocarriers generated by light irradiation in the photoconductive layer formed is insufficient therein, or at the dark portion, the charges injected from the support side cannot sufficiently be impeded, or there occurred image defects commonly called "blank areas" on the images transferred on a transfer paper which may be considered to be due to the local discharge destroying phenomenon, or image defects commonly called "white streaks" which may be considered to be caused by, for example, scraping with a blade employed for cleaning. Also, when used in a highly humid atmosphere or immediately after being left to stand in a highly humid atmosphere for a long time, so called "unclearness" was frequently observed in images obtained.
Further, when the layer thickness is as thick as ten or so microns or higher, there tend to occur such phenomena as loosening or peeling of layers from the support surface of formation of cracks in the layers with passage of time when left to stand after being taking out of vacuum deposition chamber for layer formation. These phenomena will occur particularly frequently when the support is a drum-shaped support conventionally employed in the field of electrophotography. Thus, there are problems to be solved with respect to stability with lapse of time.
Thus, it is required in designing of a photoconductive material to make efforts to solve all of the problems as mentioned above along with the improvement of a-Si materials per se.
In view of the above points, the present invention contemplates the achievement obtained as a result of extensive studies made comprehensively from the standpoint of applicability and utility of a-Si as a photoconductive member used for electrophotographic image forming members, solid stage image pick-up devices, reading devices, etc. It has now been found that a photoconductive member having a photoconductive layer comprising an amorphous layer, which comprises a-Si, particularly so-called hydrogenated amorphous silicon, halogenated amorphous silicon, or halogen-containing hydrogenated amorphous silicon which is an amorphous material containing at least one hydrogen atom (H) and halogen atom (X) in a matrix of silicon atoms (hereinafter referred to comprehensively as a-Si(H,X)), said photoconductive member being prepared by design so as to have a specific layer structure is found to exhibit not only practically extremely excellent characteristics but also to surpass the photoconductive members of the prior art in substantially all respects, especially markedly excellent characteristics as a photoconductive member for electrophotography. The present invention is based on such finding.